Internal Bit Depth Increase (IBDI) allows extending transforms precision and reference frames buffer precision and can be used for improving codecs' performances significantly.
As exemplarily depicted in FIG. 1, the principle of IBDI is to increase the original bit depth of the original frame samples VID of an InputBitDepth by bitlncrement to an increased bit depth. In the Figure, bold arrows depict flow of data of increased bit depth while normal arrows depict flow of data of original bit depth. IBDI is done prior to transforming and quantizing TQ a residual with respect to a prediction PRED for encoding ENC into a bit stream BS. For prediction, reconstructed reference frames of increased bit depth are used, the reconstructed reference frames resulting from inverse quantization and inverse transformation ITIQ and are subjected to a de-blocking and in-loop filtering FILT before being buffered BUF.
At decoder side, as exemplarily depicted in FIG. 2, an internal bit depth decrease IBDD is applied, after a bit stream BS is received, decoded DEC, inverse quantized and inverse transformed ITIQ, combined with a prediction PRED coming from a buffer BUF and filtered with the de-blocking and in-loop filtering FILT. After bit depth decrease IBDD the video is output. The decoded residuals and the reference frames used for prediction are of said increased bit depth and first a reconstructed frame of said increased bit depth is reconstructed which is then bit depth reduced to regain the frame.
The increase of bit depth can be achieved by left shifting (i.e. adding bitlncrement zeroes on the right of the sample value), for instance.